Atomic-scale imaging of structural evolution from anatase TiO2 to cubic TiO under electron beam irradiation

The introduction of oxygen vacancies into transition metal oxides can change their phases and electronic structures, subsequently impacting the physical and chemical properties. However, comprehensively understanding the phase transition process at the atomic scale remains challenging. Here, we directly image the atomic structural evolution from anatase TiO2 to cubic TiO under electron beam irradiation via in-situ scanning transmission electron microscope and electron energy loss spectroscopy, with a detailed analysis of the TiO/TiO2 interfacial structure. During this process, electron beam irradiation induces the formation of oxygen vacancies on the TiO2 surface, which drives the migration and rearrangement of Ti atoms. Theoretical and experimental methods are employed to provide insight into possible migration paths. Moreover, the formation of TiO is detected from other directions, but less distinct than that observed on the (010)TiO2 facet. This demonstrates an interesting facet dependence attributed to variations in the formation energies of surface oxygen vacancies. In addition, subsequent irradiation on TiO does not induce new structural change, but only surface roughening. Our findings offer valuable atomic-scale insights to the complex structural evolution as well as a new method to precisely manipulate phases of the transition metal oxides.